Unsheathed safety explosive composition



of a flame-quenching solid material.

Patented Oct. 7, 1952 UNSHEATHED SAFETY EXPLOSIVE COMPOSITION Arthur J.Lowe, West Kilbride, Scotland, assignor to Imperial Chemical Industriesporation of Great Britain Limited, a cor- No Drawing. Application March26, 1951, Serial No. 217,677. In Great Britain May 5, 1950 Thepresentinvention relates to the production of nitroglycerine-free ammoniumnitrate/trinitrotoluene compositions particularly suitable for use inthe production of unsheathed safety explosive cartridges.

The object of the present invention is to provide nitroglycerine-freeammonium nitrate/trinitrotoluene compositions particularly suitable foruse in the production of unsheathed safety explosive cartridges which atleast substantially approach in explosive character and in safetysheathed explosive cartridges of nitroglycerinefree type containingammonium nitrate and trinitrotoluene and common salt.

It is known that an exceptionally high degree of freedom from danger ofignition of fiery and dusty atmospheres is attained by the use of theso-called safety sheathed explosives, in which 7 Claims. (01. 52-7) thecylindrical surface of the wrapped explosive cartridge is provided withan exterior covering Although the sheathing of explosive cartridges withflame quenching materials renders it possible to employ as theflame-quenching medium certain very effective materials that cannotnormally be incorporated into the explosive composition itself and moregenerally facilitates the production of blasting cartridges having adesirable combination of safety, sensitiveness to initiations and power,the provision of an external sheath of such material and the handlingand employment of the resulting blasting cartridges entail a certainamount of inconvenience. Thus in the manufacture of safety sheathedexplosive cartridges it is necessary to accommodate the flame-quenchingmaterial either in powder form in an outer annular receptacle formedbetween the normal wrapping of the explosive cartridge and an externalcontainer of paper, or in the form of a more or less stiff structuremade with the aid of some binding or bonding medium, which can beapplied by rolling or otherwise around the normal wrapped explosivecartridge and protected by an additional outer layer of paper. Itfollows that safety sheathed explosive cartridges are of greaterdiameter than the actual cartridges of explosive embodied in them andconsequently necessitates the drilling of correspondingly widerbore-holes. Moreover, care must be taken to obviate the possibility thatsome of the flame-quenching material still finds its way in pulverulentform between the end of the normal explosive wrapper and the terminalportion of the outer wrapper of the explosive cartridge, which mightprevent end-to-end propagation of detonation when such cartridges arearranged in file in the bore-hole. It is accordingly desirable toprovide unsheathed explosive cartridges of satisfactory sensitivenessand safety characteristics comparable with those of sheathed explosivecartridges of the same power; or to provide unsheathed explosivecartridges of the same degree of safety, as indicated for instance by anunstemmed test in a gallery containing a 9% methane/air mixture ofcomparable effective power to those of sheathed explosives.

It is well-known for example that unsheathed nitro-glycerine-freeammonium nitrate/trinitrotoluene explosive cartridges made for instancefrom Douglas powder containing 15% trinitrotoluene, 69% ammonium nitrateand 16% sodium chloride, have a power equivalent to of that of blastinggelatine as observed in the ballistic pendulum and are in themselvessafety explosives, and that when such explosive cartridges are sheathedso that the sheathed cartridges have in effect a power of about 43% ofthat of blasting gelatine they exhibit that greater degree of safetywhich may be called for in many mining operations.

We have now found that it is possible to make nitroglycerine-freeammonium nitrate/trinitrotoluene compositions particularly suitable forthe production of unsheathed explosive cartridges having a degree ofsafety at least approaching that of said sheathed explosive cartridgesmade from Douglas powder and likewise having a power in the region of43% of that of blasting gelatine if said compositions include asadditional major constituents both sodium chloride and sodium nitrateand if the four major constituents, trinitrotoluene, ammonium nitrate,sodium nitrate and sodium chloride lie within certain ascertainedgravimetric limits.

According to the present invention safety explosive compositionsconsisting of a mixture of trinitrotoluene, ammonium nitrate, sodiumnitrate, and sodium chloride as major ingredients. having abulk densityof 0.90 to 1.05 gm./co. at 25 lbs. pressure per sq. in., and having acalculated oxygen balance between -0.5 and +3 gms. oxygen per gms. ofthe composition are characterised in that the percentage by weight oftrinitrotoluene is between 11 and 22%, of ammonium nitrate is between 22and 36%, of sodium nitrate is between 12 and 27% and of sodium chlorideis between 29 and 35%.

If desired the safety explosive compositions of the present inventioncan include up to 3% of oxidizable organic materials as for examplevegetable tissue materials, preferably of low density, for instancebalsa woodmeal or ground cork; such materials as organic dyestuffs ofsulphonated character, for instance Acid Magenta and salts oftri-sulphonated New Magenta which may be present in very smallquantities on the surface of the ammonium nitrate as an antisettingagent, or incorporated into the explosive composition as such may alsobe reckoned as an oxidizable organic material for this purpose, as mayother organic ingredients which are not of vegetable tissue nature butwhich may be present as minor constituents.

For the compositions of the present invention to have the bulk densityspecified they can be prepared in known manner by mixing the ingredientsby dry milling with attrition and thereafter moistening sufliciently togive the mixture a moisture content of approximately 1% and dryingwithout mechanical agitation at a temperature exceeding the transitionpoint of ammonium nitrate at 32.2 0., allowing the mixture thus producedto cool and finally screening the resulting pulverulent material.

In adjusting the oxygen balance for any proposed explosive compositionthe oxygen requirements of the various organic constituents may becalculated if necessary after performing an elementary analysis of thematerial on the basis that the carbon is to be oxidized to carbondioxide and the hydrogen to water and any nitrogen is to be liberated aselementary nitrogen, due allowance being made for any water content inthe original material.

In putting the invention into effect any lumps of the final materialretained on the screen may be broken down mechanically by light pressureinto powder. A relatively coarse screen may be used for this purposealthough the product is a relatively fine powder, which when packed intopre-formed paper cartridge cases in known man ner has a density ofapproximately 1 gram per 00., tending to be a little higher than thisfigure in the absence of low density vegetable tissue material and alittle lower when such material is included. It may be noted that theexplosives provided according to the present invention need not containany ingredients that are difficult to obtain in a satisfactory conditionfrom the point of view of the thermal stability of the explosivecomposition as indicated by the Abel heat test.

We have found that if explosive compositions consisting of a mixture toftrinitrotoluene, ammonium nitrate, sodium nitrate and sodium chloride asmajor ingredients, have these ingredients in quantities outside thelimits specified for the compositions of the present invention althoughhaving the bulk density and oxygen value ing or are not as safe as thesafety sheathed explosive cartridges of the nitroglycerine-free typecontaining ammonium nitrate, trinitrotoluene and common salt.

We have also found that it is necessary to adhere to the limitsspecified for the bulk density of the compositions of the presentinvention in order that the said compositions should have the requireddegree of sensitivity to initiation and propagation.

Furthermore it is well-known in order that safety explosive compositionsconsisting of a mixture of trinitrotoluene, ammonium nitrate, and sodiumchloride should not give off poisonous fumes on initiation that thesecompositions should have a calculated oxygen balance between -0.5 and +3gms. oxygen per gms. of the composition.

It is also often desirable to include in such compositions up to 3% offibre in order to lower the bulk density of the compositions.

From the stipulated oxygen balance of 0.5 to +3 gms. oxygen per 100 gms.of the composition it can be deduced that the percentage, by weight oftrinitrotoluene must be between 11 and 22% and having regard to thetotal quantity of flame-quenching ingredients of a sheathed explosive ofthe non-nitroglycerine trinitrotoluene/ammonium nitrate type, it can beassumed that the sodium chloride content should be in the region of 33%.

In view of the high proportion of common salt which it may thus bepossible to include, it becomes impossible to obtain the required oxygenbalance with ammonium nitrate as the only oxygen giving salt. It thusbecomes necessary to include a salt yielding more oxygen per; unitweight than ammonium nitrate, and for -commercial reasons sodium nitrateis the salt chosen for this purpose. From general considerations it isdeducible that the sodium nitrate content should be between 14 and 25%.From this it can be easily deduced that the ammonium nitrate content isto be between 20 and 42%. It can also be deduced by calculation that ifa composition containing as major ingredients trinitrotoluene, ammoniumnitrate, sodium nitrate, and common salt, is to approach in power 43% ofthat of blasting gelatine the ammonium content must be not less than 22%and not more than 42%.

The following table embodies experimental data which indicate that thelimits specified for the major ingredients of the compositions of thepresent invention are essential if these compositions are to satisfy therequirements of safety, power, and oxygen value. I

A positive sign indicates that the gas test has been passed with respectto safety. A negative sign indicates that the gas test has not beenpassed with respect to safety.

Experimental examples Composition No. l 2 3 4 5 6 7 3 9'lrinitrotoluene, percent l8 l7. 5 l8 l3 18 20 15 15 15 Ammonium nitrate20 25 30 35 28 24 39 41 34 Sodium nitrate. 30 20 20 20 22 25 10 12 18Common salt. 30 36 32 29 30 30 35 3 23 Balsa 2 1. 5 3 2 1 1 2 3 Power(actual). 35. 9 35. 3 40. 6 40. 4 40. 4 41. l 41. 4 45. 8 43. 6 Bulkdensity l- 03 1. 02 1. 05 0. 92 1. 04 1.10 l. 04 0. 98 0.99 Oxygen value+2- 3 -0. 5 +2. 1 +3. 0 +0. 1 -o. 5 +0. 8 2 5 Safety in gas testspecified for the compositions of the invention, they are either tooweak for practical coal min- In the above table those compositionshaving a power less than 36% of blasting gelatine are unsuitable as theyare not sufliciently powerful for practical coal mining.

If the compositions numbered 3 to are made so that they have a bulkdensity greater than 1.05 at 25 lbs. per sq. in., they haveexperimentally been found to be unsafe in accordance with the gas test.The lower limit of 0.90 at 25 lbs. per sq. in., for the bulk density ofthe compositions of the present invention is one which is known to bethe lowest obtainable under manufacturing conditions.

' Compositions in accordance with the invention are illustrated by thefollowing examples, in which the parts and percentages mentioned are byweight.

Example 1 18 parts flake TNT and 18 parts dried ammonium nitrate aremilled together in a suspended steel edge-runner mill until the discreteparticles of TNT are no longer visible to the naked eye. A further partsdried ammonium nitrate and 22 parts sodium nitrate and thereafter insuccessive stages, 30 parts sodium chloride and 2 parts balsa woodmealare introduced, the milling being continued for a period sufficient toensure that the TNT and the inorganic nitrates are reduced to a finepowder and thoroughly incorporated in known manner. It is desirable toadd the balsa wood meal at a late stage of the incorporation.Thereafter, sumcient water is added to bring the moisture content to 1%and the water is dispersed through the composition by continuing themilling for a short period. The thus moistened powder is shovelled on toaluminium trays, which are carried to a drying room in which they areexposed to a current of warm air, the ambient temperature in the roombeing about 50 C. When the material, which constitutes a powder, isthoroughly dry it is screened through a mesh British StandardSpecification screen and any remaining lumps are subjected to lightimpact on the screen with wooden balls,

- which causes them to fall to a fine powder which will join that whichhas already passed through the screen.

The explosive powder so obtained is fed under very light pressure intopre-formed paper cases of 1%," or 1 diameter giving cartridges of weightfrom 2-8 ozs. as may be required. The oxygen value of the composition is+0.1. Its density at 25 lbs. pressure is 1.04 grams per cubiccentimetre.

A No. 2 mercury fulminate/potassium chlorate detonator is found to besufilcient to initiate the fresh dry explosive cartridge of 1%"diameter, but in service it will be understood a No. 6 or No. 8detonator, which may conveniently be a lead azide/lead styphnate/tetryldetonator having a copper alloy casing, is normally employed.

The power of the explosive is 40.4% of that of blasting gelatine asmeasured by the ballistic pendulum. In a double cartridge test in whichtwo cartridges each of 1%" diameter and 3" length are disposed in anempty paper tube in alignment along their longitudinal axis with theirends separated by an air gap, and one of the cartridges is initiatedfrom its remote end by a No. 8 detonator, it is found that the secondcartridge detonates satisfactorily when the gap'is 1" but fails when itis 1.5" long. The velocity of detonation measured in a cartridge of 1diameter and 8" length is 1950 metres per second. In an unstemmed testin an explosive gallery with inverse initiation in a 9% methane/airatmosphere (by volume) unsheathed cartridges of the explosive of 1%"diameter are found to have a charge limit between 16 and 20 ozs.

The charge limit in a similar test of a normally made exposivecomposition not in accordance with the invention known as Douglas powderand containing 15% TNT, 69% ammonium nitrate and 16% sodium chloridesheathed with 30% sodium bicarbonate powder is between 12 and 16 ozs. ofexplosive. This Douglas powder gives a power in its sheathed conditionequivalent to 43% of that of blasting gelatine as observed in theballistic pendulum, and with unsheathed gives a power equivalent to 65%of that of blasting gelatine. Its velocity of detonation is 3,500 metresper second.

Example 2 The ingredients of the explosive composition are as follows:

Per cent TNT 18 Ammonium nitrate 30 Sodium nitrate 20 Sodium chloride 32The manner of mixing the explosive is similar to that in Example 1 andit is cartridged in the same way. The resulting explosive has an oxygenvalue of +2.1 grams per grams explosive and its density is 1.05 gram-sper cc. Its power is 40.6% of that of blasting gelatine. The driedexplosive freshly made can be initiated by a No. 1 detonator. Itsvelocity of detonation is 2,200 metres per second, and in the doublecartridge test the second of the cartridges detonates when separatedfrom the first by a gap of 1 /2" but fails to do so when the gap is 2".In the gallery test referred to in Example 1 the charge limit is between10 and 12 ozs.

Example 3 The ingredients of the explosive composition are as follows:

Per cent TNT 13 Ammonium nitrate 35 Sodium nitrate 20 Sodium chloride 29Balsa woodmeal 3 The oxygen value of the resulting explosive powder,which is made after the fashion described in Example 1, is +3.0 gramsoxygen per 100 grams explosive and its density is 0.92 grams per cc. Itspower as measured in the ballistic mortar is 40.4% of that of blastinggelatine and in the double cartridge it gives the same figures as theexplosive of Example 1. The explosive when freshly made and dried issensitive to a No. 2 detonator. Its velocity of detonation is 2,150metres per second and in the gallery test referred to in Example 1 thecharge limit of a 11%" diameter unsheathed cartridge is not less than 18ozs.

What I claim is:

1. Safety explosive compositions consisting of a mixture oftrinitrotoluene, ammonium nitrate, sodium nitrate, and sodium chlorideas major ingredients, having a bulk density of 0.90 to 1.05 gram per cc.at 25 lbs. pressure per sq. in., and having a calculated oxygen balancebetween 0.5 and +3 grams oxygen per 100 grams of the compositioncharacterized in that the percentage by weight of trinitrotoluene isbetween 11 and 22%, of ammonium nitrate is between 22 and 36%, of Sodiumnitrate is between 12 and. 27%, and of sodium chloride is between 29 and35%.

'2 Safety explosive compositions as claimed in claim 1 which include upto 3% of oxidizable organic materials.

3. Safety explosive compositions as claimed in claim 2 wherein theoxidizable organic materials are vegetable tissue materials.

4. Safety explosive compositions as claimed in claim 3 wherein thevegetable tissue materials are of low density.

5. Safety explosive compositions as claimed in claim 4 wherein thevegetable tissue material'of low density is balsa woodmeal.

6. Safety explosive compositions as claimed in 15 claim 4 wherein thevegetable tissue material is ground cork.

8 V 7; Safety. explosive compositions as claimed in claim 2 wherein theoxidizable organic materials are sulfonated organic dyestuffs.

ARTHUR J. LOWE. 4

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

1. SAFETY EXPLOSIVE COMPOSITIONS CONSISTING OF A MIXTURE OFTRINITROTOLUENE, AMMONIUM NITRATE, SODIUM NITRATE, AND SODIUM CHLORIDEAS MAJOR INGREDIENTS, HAVING A BULK DENSITY OF 0.90 TO 1.05 GRAM PER CC.AT 25 LBS. PRESSURE PER SQ. IN., AND HAVING A CALCULATED OXYGEN BALANCEBETWEEN -0.5 AND +3 GRAMS OXYGEN PER 100 GRAMS OF THE COMPOSITIONCHARACTERIZED IN THAT THE PERCENTAGE BY WEIGHT OF TRINTROTOLUENE ISBETWEEN 11 AND 22%, OF AMMONIUM NITRATE IS BETWEEN 22 AND 36%, OF SODIUMNITRATE IS BETWEEN 12 AND 27% AND OF SODIUM CHLORIDE IS BETWEEN 29 AND35%.